A paper cup first last piece comparison can reveal movement across a production run, but two isolated cups rarely explain when or why the change occurred. Startup stabilization, material splices, operator interventions and planned shutdown behavior must be separated from gradual process drift.
This guide supports comparative production studies. It does not define universal sampling times, tolerances or machine settings. Use the approved product drawing, control plan and supplier instructions.
Diagnostic decision table
| Observed result | Required follow-up | Do not assume |
|---|---|---|
| First cup differs | Review stabilization and startup rejects | Steady production has the same condition |
| Last cup differs | Check time trend and shutdown actions | Wear is the only cause |
| Both endpoints agree | Inspect intermediate samples | The entire run was stable |
| One dimension moves | Review related functional responses | A tooling adjustment is automatically required |
Define operational start and end points
Define when the run begins for analysis: first machine cycle, first cup after startup checks or first accepted steady-state cup. Define the last comparison point before operators reduce speed, empty material or change settings. These definitions prevent transition material from being labelled as normal production.
Record machine, tooling, SKU, board lot, coating, operator and preceding downtime. Preserve rejected startup cups separately. If the comparison is intended to study warm-up, include the transition deliberately rather than removing it from the record after results are known.
Collect time-linked samples across the run
Take identified groups at the start, planned intermediate times and the end. Keep forming position and material splice information. A start-and-end pair can miss a temporary excursion that recovered before shutdown, so intermediate evidence is necessary for a meaningful stability claim.
Use the same sample count and handling at each point. Avoid nesting one group under heavier pressure or measuring the first group immediately while the last group conditions overnight. Store samples so the comparison reflects production time rather than different post-production treatment.
Use unchanged measurement and test methods
Measure defined dimensions and functional characteristics with the same fixture, instrument, orientation and operator plan. Randomize measurement order where practical so instrument drift does not align with production time. Retain raw readings and invalid-test reasons.
Review measurement repeatability before interpreting a small endpoint difference. A flexible cup may respond to contact pressure or conditioning. Do not add decimal places or average unrelated orientations to make the result appear more sensitive than the verified method.
Plot the time sequence and process events
Display individual or subgroup results in production order and annotate material changes, stops, alarms, adjustments and maintenance. Look for gradual movement, steps and isolated events. A first-versus-last average alone cannot distinguish these patterns.
Compare multiple runs before calling a repeatable drift mechanism. If the condition follows a material lot or forming position rather than elapsed time, investigate that source. Do not adjust heating, pressure or timing until the observed pattern and authorized control range have been reviewed with HANNAI.
Verify correction on a new representative run
After an approved correction, repeat the original sampling and methods without selecting only favorable endpoints. Confirm steady production, transition behavior and the intended product functions. Keep the original run as comparison evidence.
Send HANNAI the time chart, process-event log, sample identities and before-and-after results. This evidence supports targeted review of warm-up, tooling, material and handling while avoiding a conclusion based on two convenient cups.
Related equipment and next checks
Review the HN-M100 automatic paper cup machine and the related guide to cold and warm restart reject analysis. The Engineering Notes archive connects these checks with wider machine planning.
Frequently asked questions
Are the first and last cups enough to prove run stability?
No. Include planned intermediate evidence and process events.
Should startup rejects be mixed with accepted production?
Keep them identified according to the approved startup rule.
Can samples be measured under different conditioning?
Use controlled, comparable handling and conditioning.
Does endpoint movement prove tooling wear?
Review time, material, station and measurement evidence before assigning cause.
Review the evidence with HANNAI
Send your machine model, component identification and the observations described in this guide. Include the drawing or material reference and any before-and-after measurements so the required next check can be identified.